XVI International Botanical Congess

Volvocine algae range in size and complexity from unicellular Chlamydomonas to multicellular Volvox, which exhibits a division of labor between small, biflagellate somatic cells and large, non-motile reproductive cells called Agonidia.@ In small volvocine algae (Chylamydomonas to Pandorina) all cell execute the motile and reproductive functions sequentiallly, but with increasing size (Eudorina to Volvox) comes an increasing tendency to differentiate two cell types that divide these labors. In V. carteri this germ-soma division of labor is completed by setting apart the two cell types in very early development by asymmetric cell division. Mutational analysis indicates that three kinds of V. carteri gene products convert the ancestral Afirst somatic and then reproductive@ developmental program into a germ-soma dichotomy: first the Gls proteins mediate asymmetric division and formation of large and small cells, the Lag proteins act in large cells to repress somatic functions while the RegA protein acts in small cells to repress reproductive functions. These mechanisms are being eluciadated, and their evolutionary origins are being explored.